Cathodes for electron tubes



Sept. 13, 1955 w w o 2,717,975

CATHODES FOR ELECTRON TUBES Filed March 50 1951 IN VE/VTOR WELT/S W/HTOLBY W R/VEYS United Srtates Patent CATHODES FOR ELECTRQN TUBES WeltisWihtol, Redwood City, (Ialif.

Application March 30, 1951, Serial No. 218,383

2 Claims. (Cl. 313-631) This invention relates generally to cathodes forelectron tubes.

It is a particular object of this invention to provide a self-heatedcathode having a particular utility in electron tubes havingconcentrically arranged electrodes.

It is another object of this invention to provide a cathode forconcentrically arranged electrodes which heats very rapidly whereby thecathode heating current may be turned off during standby periods withoutexperiencing the usual long heat-up time.

It is a further object of this invention to provide a self-heatedcathode structure for concentrically arranged electron tubes having goodmechanical strength and the ability to withstand frequent heatings andcoolings without substantial change in the positioning of the varioustube elements.

These and other objects of the invention will appear from the followingdescription in connection with the accompanying drawings whichillustrate one embodiment of the invention and in which Fig. 1 is a topplan View showing the improved selfheated cathode structure;

Fig. 2 is a detailed longitudinal sectional view substantially on theline 22 of Fig. 1; and

Fig. 3 is a detailed cross-sectional view substantially on the line 33of Fig. 2.

The invention is illustrated showing only a portion of ,the electrontube in which the self-heated cathode is to be used with all of theremaining elements of the electron tube eliminated for simplicity ofunderstanding.

The improved cathode structure is illustrated in association with theusual re-entrant stem (Fig. 2) of an electron tube. Two laterally spacedcathode supports 11 and a center cathode supporting rod 12 are fused tothe stem 10. The center rod 12 is located between the two laterallyspaced cathode supports 11 and extends upwardly beyond the upper ends ofthe outer rods 11, as appears in Fig. 2. The upper ends of cathodesupports 11 are displaced inwardly, as appears in Fig. 2.

Means are provided upon the supports 11 and 12 to mount a tubularcathode. These means include a mounting ring 13 and an eyelet 14 spacedapart longitudinally. The mounting ring 13 is arranged coaxially withthe center supporting rod 12, and is aflixed to the inwardly displacedupper ends of the rods 11. The eyelet 14 is secured to the upper end ofsupporting rod 12 and it comprises a cylindrical portion 15, a flange 16and a cylindrical portion 17. The cylindrical portion is secured2,717,975 Patented Sept. 13, 1955 ICC to the upper end of supporting rod12. The outer diameter of the cylindrical portion 17 is the same as theouter diameter of the ring 13.

A tubular cathode 18 is secured to and extends between the cylindricalportion 17 of the eyelet 14 and the ring 13. The cathode is preferablymade of thin metal, such as tantalum having a thickness of .0005. Itshould be proportioned so that its operating temperature is in the rangeof approximately 1000 Kelvin and it is heated not quite toincandescence.

The cathode supports 11 are used as the cathode lead and one heater leadand the cathode support 12 is used as the other heater lead.

A circular heat shield 19 is secured to the rods 11 to shield the stem10 from radiation within the tube.

In actual practice it has been found that the cathode of this inventionwill reach operating temperature in approximately /2 of a second insteadof the usual minute. This greatly reduces the standby problems and tendsto lengthen tube life.

This application describes the preferred embodiment of this inventionand is merely illustrative. This application contemplates such changesas fairly fall within the scope of the appended claims.

I claim:

1. A uniformly heated cylindrical cathode structure for an electron tubehaving a low noise factor including a first cylindrical support, asecond cylindrical support, said first and second cylindrical supportsbeing of the same diameter and arranged coaxially with respect to andlongitudinally spaced from one another, a thin metallic self-heatedcathode tube less than .001 inch thick having an operating temperatureof the order of 1000 Kelvin and being connected to the exterior of andextending between said cylindrical supports, and two heater leads, onelead being connected to said first cylindrical support and the otherlead being connected to said second cylindrical support.

2. A uniformly heated cylindrical cathode structure for an electron tubehaving a low noise factor including a first cylindrical support, asecond cylindrical support, said first and second cylindrical supportshaving the same diameter and being arranged coaxially with respect toand longitudinally spaced from one another, a thin metallic self-heatedcathode tube having a thickness of the order of .0005 inch and beingconnected to the exterior of and extending between said cylindricalsupports, and two heater leads, one lead being connected to said firstcylindrical support and the other lead being connected to said secondcylindrical support.

References Cited in the file of this patent UNZTED STATES PATENTS1,881,644 Jones Oct. 11, 1932 1,897,229 Bohm Feb. 14, 1932 1,954,203Gurtler Apr. 10, 1934 2,269,081 Felsner Ian. 6, 1942 2,468,736 ButlerMay 3, 1949 2,473,550 Spencer June 21, 1949 2,587,169 Kivari Feb. 26,1952 2,614,942 Loosjes Oct. 21, 1952

